One of the arguments against ID cards is the possibility of discrimination. For proof, you need look no further than Lebanon, where ID cards were the equivalent of death warrants. According to the BBC News article:

During the civil war, which lasted through the 1970s and 1980s, different militias aligned with various religious groups would set up checkpoints and ask for the identity cards of those who tried to pass. People would often be shot on the spot if their documents revealed the “wrong” sort of religious affiliation.